Towards the Mechanism(s) of Early Transition Metal Promoted Selective Olefin Oligomerisation Catalysis - Synthesis, Spectroscopic and XAFS Studies

寻求更高选择性、更清洁和更有效的催化剂，例如用于烯烃三聚或四聚的催化剂，仍然是化学工业的高度优先事项。实现这些目标需要详细了解催化循环和活性物质的性质。在均相催化循环中的各个阶段的表征不容易实现，因为活性物质可能是高度反应性的，并且通常是非常短暂的，使得它们的晶体学表征非常不可能。此外，对于顺磁性例如基于Cr的催化剂，NMR光谱法不能提供信息。在这个项目下，我们将开发和使用一个独特的冷冻淬火细胞，使瞬态和活性物种被困在各个选定的阶段通过循环，允许在原位光谱分析扩展X射线吸收精细结构（EXAFS）和X射线吸收近边结构（XANES）光谱技术。我们将在一组选定的N-、S-、N/S-和N/P-供体配体的存在下制备和合成一系列基于Cr、Mo和Sc的相关金属配合物，包括工业上重要的NH（CH 2CH 2Sdecyl）2和iPrN（PPh 2）2的配合物。使用一系列技术（紫外可见，EPR，45 Sc NMR光谱），结合XAFS和XANES数据，使用上述设置，我们将通过活化和催化详细探测各个阶段的氧化态和结构，以提供对工作机制的更详细的理解。我们还希望展示新的快速（毫秒）冷冻淬火XAFS/XANES方法的潜力更广泛地提供有关其他均相催化系统的关键信息。

The quest for more highly selective, cleaner and more efficient catalysts e.g for olefin trimerisation or tetramerisation remains a high priority for the chemical industry. Achieving these targets demands a detailed understanding of the catalytic cycle(s) and the nature of the active species. Characterisation of the individual stages in a homogeneous catalytic cycle is not easily achieved since the active species are likely to be highly reactive and often very transient, making their crystallographic characterisation highly unlikely. Furthermore, for the paramagnetic e.g. Cr-based catalysts NMR spectroscopy is not informative. Under this project we will develop and use a unique freeze-quench cell to allow the transient and active species to be trapped at various selected stages through the cycle, allowing in situ spectroscopic analysis by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopy techniques. We will prepare and characterise a series of related metal complexes based on Cr, Mo and Sc in the presence of a selected set of N-, S-, N/S- and N/P-donor ligands, including complexes of the industrially important NH(CH2CH2Sdecyl)2 and iPrN(PPh2)2. Using a range of techniques (UV-visible, EPR, 45Sc NMR spectroscopy), in conjunction with XAFS and XANES data using the set-up described above, we will probe in detail the oxidation state and structures at various stages through the activation and catalysis to provide a much more detailed understanding of the mechanisms at work. We also expect to demonstrate the potential of the new rapid (millisecond) freeze-quench XAFS/XANES approach much more widely to provide key information regarding other homogeneous catalysis systems.